The present invention relates generally to semiconductor-based light emitting devices, and, more particularly, to a structure of such devices and a method for manufacturing the same.
A Light-emitting diode (LED) is a semiconductor diode based light source. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. When used as a light source, the LED presents many advantages over incandescent light sources. These advantages include lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability.
FIG. 1 is a perspective view of a LED die 100 which comprises a substrate 102, an N-type layer 110, a light-emitting layer 125 and a P-type layer 130. N-contact and p-contact 115 and 135 are formed on the N-type layer 110 and the P-type layer 130, respectively, for making electrical connections thereto. When a proper voltage is applied to the N- and P-contacts 115 and 135, electrons depart the N-type layer 110 and combine with holes in the light-emitting layer 125. The electron-hole combination in the light-emitting layer 125 generates light. Sapphire is a common material for making the substrate 102. The N-type layer 110 may be made of, for example, AlGaN doped with Si or GaN doped with Si. The P-type layer 240 may be made of, for example, AlGaN doped with Mg or GaN doped with Mg. The light-emitting layer 125 is typically formed by a single quantum well or multiple quantum wells, e.g. InGaN/GaN.
In some cases, a series or parallel LED array is formed on an insulating or highly resistive substrate (e.g. sapphire, SiC, or other III-nitride substrates). The individual LEDs are separated from each other by trenches, and interconnects deposited on the array electrically connect the contacts of the individual LEDs in the arrays. Typically, to make sure complete electrical isolation of individual LEDs, a dielectric material is deposited over the LED array before the interconnects deposition, then patterned and removed in places to open contact holes on N-type layer and P-type layer, such that dielectric material is left in trench between the individual LEDs on the substrate and on the mesa walls between the exposed P-type layer and N-type layer of each LED. Dielectric material may be, for example, oxides of silicon, nitrides of silicon, oxynitrides of silicon, aluminum oxide, or any other suitable dielectric material.
However, deposition of dielectric material is a slow and costly process. Moreover, subsequently formed interconnects which poses reliability concern due to complex profiles and sharp corners of the interconnects. As such, what is desired is a system and method for manufacturing a LED array device cost-effectively and with improved long term reliability.